Progress in Metal-Organic Frameworks Facilitated Mercury Detection and Removal
Round 1
Reviewer 1 Report
Metal organic frameworks (MOFs) are a kind of star material of modern material science. The manuscript systematically summarized the MOFs-based assays/sensors for detection and removal of elemental mercury and Hg2+ ions, which provides valuable information on the mechanisms or adsorption isotherms of MOFs towards Hg2+ ions. The manuscript is well writing, which could be published as it.
- There are several reviews on same topic (such as, JOURNAL OF THE ELECTROCHEMICAL SOCIETY 168(2021)037513, MOLECULES 25(2020)513, COORDINATION CHEMISTRY REVIEWS 408(2020)213191, and COORDINATION CHEMISTRY REVIEWS 358(2018)92-107), which should be cited.
- For comparison, the performances (such as, detection limit, dynamic ranges, MOF types, detection principles) of MOF-based Hg sensors/assays should be summarized in a table.
Author Response
Reviewer 1:
Metal organic frameworks (MOFs) are a kind of star material of modern material science. The manuscript systematically summarized the MOFs-based assays/sensors for detection and removal of elemental mercury and Hg2+ ions, which provides valuable information on the mechanisms or adsorption isotherms of MOFs towards Hg2+ ions. The manuscript is well writing, which could be published as it.
“Author Response”
We are very thankful to the reviewer, for providing the valuable comments which enhance the quality of our manuscript. As per reviewer’s comments, we have revised the manuscript and rectified those technical and formal flaws.
- There are several reviews on same topic (such as, JOURNAL OF THE ELECTROCHEMICAL SOCIETY 168(2021)037513, MOLECULES 25(2020)513, COORDINATION CHEMISTRY REVIEWS 408(2020)213191, and COORDINATION CHEMISTRY REVIEWS 358(2018)92-107), which should be cited.
“Author Response”
As suggested by the reviewers those references were cited as Refs 6, 22-24.
- For comparison, the performances (such as, detection limit, dynamic ranges, MOF types, detection principles) of MOF-based Hg sensors/assays should be summarized in a table.
“Author Response”
We agree that providing such comparative table might enhance the manuscript clarity. However, it will also lengthen the pages of the review and affect the readers visibility. Moreover, we have already provided the required information in the text. Thereby addition of comparative table will provide duplicated information in manuscript.
Reviewer 2 Report
The review article topic on Progress in metal-organic frameworks facilitated mercury detection and removal is the good topic selected by authors. However, this review articles lack in several ways. Need major revision for reconsideration.
- Under abstract section I can feel author have mention about Metal organic Frameworks (MOFs) are noted as exceptional candidates towards the detection and removal of specific analytes. After going through this review manuscript it was very clear that this review script focusing on MOFs in mercury detection and removal. This is interesting review article but few suggestion are provided for authors. How the present review script gain novelty?
- Provide the clear motivation for choosing the MOFs for mercury detection.
- There are so many other types of metals are available , while the focus of authors are only on mercury detection and removal. What about the others such as Cr(VI), As(III), Cd(II), Pb(II) etc.
- On page 2, authors have mention “Therefore, U. S. Environmental Protection Agency (EPA) regulated an allowable maximum level of mercury of 2 ppb (10 nM) in the drinking water and 3 ppm (1.5 μM) in fish tissue” Provide with the relevant references.
- Provide the reason why the metal organic frameworks (MOFs)-based probes towards specific analytes discrimination are highly anticipated with real time applications.
- There are so many types of adsorbents and sensors are used for removal and detection of mercury? Why the author have targeted MOFs in present review script.
- Please write your text in good English (American or British usage is accepted, but not a mixture of these). English language manuscript require editing to eliminate possible grammatical or spelling errors and to conform to correct scientific English.
- Discuss the advantages of MOFs with that of other reported adsorbents and sensor materials in literatures for Mercury detection and removal.
- Provide the impact of mercury on living beings and ecosystem.
- What is the advantages of synthesis of MOFs based on Microwave method. Few MOFs synthesis by microwave methods in the literatures need to be discuss under section 3 Synthetic tactics involved in MOFs construction.
- Kindly confirm all the figures used in this script have copyright permission.
- In page 31, author have mention “1. Majority of MOFs and their derivatives detect or adsorb the Hg species in aqueous media, therefore, MOFs-based experiments could sustain the eco-friendly process”. Justify?
- Conclusions and Perspectives need to be shorten.
Author Response
Reviewer 2:
The review article topic on Progress in metal-organic frameworks facilitated mercury detection and removal is the good topic selected by authors. However, this review articles lack in several ways. Need major revision for reconsideration.
“Author Response”
We are very grateful to the reviewer for providing the opportunity to clarify our results, which improve the standard of this article.
- Under abstract section I can feel author have mention about Metal organic Frameworks (MOFs) are noted as exceptional candidates towards the detection and removal of specific analytes. After going through this review manuscript it was very clear that this review script focusing on MOFs in mercury detection and removal. This is interesting review article but few suggestion are provided for authors. How the present review script gain novelty?
“Author Response”
Over the past hundred years, the amount of mercury in the upper 100 meters of the world ocean has doubled. The mercury contents in fishes and human hairs in the different countries around the world regularly exceed the maximal levels recommend by the WHO. Therefore, development of sensors of this toxic analyte is an important topic in sensing science. Among various adsorbents and probes, MOFs-based mercury detection seems to be exceptional. However, valuable information which was missing in earlier reviews has been well presented and delivered in this review. Thereby the novelty has been well established.
2. Provide the clear motivation for choosing the MOFs for mercury detection.
“Author Response”
The motivation for choosing MOF for mercury detection is clearly demonstrated in the introduction (pages 1 and 2).
3. There are so many other types of metals are available, while the focus of authors are only on mercury detection and removal. What about the others such as Cr(VI), As(III), Cd(II), Pb(II) etc.
“Author Response”
We agree that there are so many toxic metal ions can be detected and removed by MOF, but only very limited reports were available on the MOF-based mercury detection, which motivated us to deliver this review. Moreover, there are already many reviews available with MOFs for other toxic metal ions (Cr(VI), As(III), Cd(II), Pb(II), etc.). Therefore, they were not included in this review.
4. On page 2, authors have mention “Therefore, U. S. Environmental Protection Agency (EPA) regulated an allowable maximum level of mercury of 2 ppb (10 nM) in the drinking water and 3 ppm (1.5 μM) in fish tissue” Provide with the relevant references.
“Author Response”
As per suggestion, the references are cited in the revised version.
5. Provide the reason why the metal organic frameworks (MOFs)-based probes towards specific analytes discrimination are highly anticipated with real time applications.
“Author Response”
This is because majority MOFs displayed the aqueous solubility with enhances stability and also possess exceptional opto-electronic properties. Therefore, MOFs-based probes towards specific analytes discrimination are highly anticipated with real time applications.
6. There are so many types of adsorbents and sensors are used for removal and detection of mercury? Why the author have targeted MOFs in present review script.
“Author Response”
We agree that there are so many types available for mercury detection and removal. We have chosen the MOFs for this review because of their exceptional aqueous solubility, stability and opto-electronic properties. Moreover, reviews on MOFs-based mercury detection was not up to date, which allowed us to deliver this review.
7. Please write your text in good English (American or British usage is accepted, but not a mixture of these). English language manuscript require editing to eliminate possible grammatical or spelling errors and to conform to correct scientific English.
“Author Response”
We have corrected the lingual deficiencies as per the reviewer’s suggestion.
8. Discuss the advantages of MOFs with that of other reported adsorbents and sensor materials in literatures for Mercury detection and removal.
“Author Response”
Advantages and limitations for MOFs-based mercury detection and removal are provided in section 12 and 13. Since our review is focused on the current progress, it is not necessary to compare with other adsorbents. Moreover, our intention is not to justify the MOFs as best adsorbents compared to other existing tactics. Thereby this comparison is omitted in this review.
9. Provide the impact of mercury on living beings and ecosystem.
“Author Response”
Impact of mercury on living beings and eco system is provided in the introduction (see first paragraph) as follows.
“Upon accumulation of mercury in environmental water, it sedimented and converted as toxic methylmercury, which enters the food cycle to cause serious diseases in living beings as stated next [6]. Accumulation of mercury in human body may lead to various health issues, such as brain damage, central nervous syndromes, Minamata disease, cognitive and motion disorders, etc. [7-9]”
10. What is the advantages of synthesis of MOFs based on Microwave method. Few MOFs synthesis by microwave methods in the literatures need to be discuss under section 3 Synthetic tactics involved in MOFs construction.
“Author Response”
As suggested by the reviewer, advantages of synthesis of MOFs based on the microwave method has been discussed further with certain literatures.
11. Kindly confirm all the figures used in this script have copyright permission.
“Author Response”
Yes, we have already got the copyright permission for all the figures as stated in the text.
12. In page 31, author have mention “1. Majority of MOFs and their derivatives detect or adsorb the Hg species in aqueous media, therefore, MOFs-based experiments could sustain the eco-friendly process”. Justify?
“Author Response”
The text has been revised as “Majority of MOFs and their derivatives detect or adsorb the Hg species in aqueous media, therefore, MOFs-based detection and removal experiments could sustain the eco-friendly process via decontaminating the toxic mercury from aquatic environment.”
13. Conclusions and Perspectives need to be shortened.
“Author Response”
As per suggestion, in conclusions and perspectives, two points (5 and 15) has been removed and contents has been shortened.
Reviewer 3 Report
Recommendation: The manuscript may be publishable after a major revision.
The review of Kien Wen Sun and co-workers is focused on the detection and removal of mercury ions using MOFs. Mercury is one of the most toxic substances. Inorganic mercury compounds are the most prevalent. Hg2+ ions are bound by both inorganic and organic ligands, and can undergo methylation reaction. Over the past hundred years, the amount of mercury in the upper 100 meters of the world ocean has doubled. The mercury contents in fishes and human hairs in the different countries around the world regularly exceed the maximal levels recommend by the WHO. Thus, development of sensors of this toxic analyte is actual topic in sensing science. The authors carefully look through the recent literature and tried to summarize the reported data. Unfortunately, despite the interest of the topic and excellent list of the references, I cannot recommend this review for publication in the present form. Moreover, I think that in its current state it has serious problems that will take significant efforts to rectify.
The main problem is that the authors use a descriptive discussion of MOF structures and their actions which is insufficient for modern science. In the best case, the brutto formula of MOFs or metal nodes are given and ligands are named. As a result, a reader has no full information on the organization of the solid. The authors should complete the manuscript by schematic presentation of ALL MOFs and schemes which will allow to understand their synthesis and sensing properties. Please, look through the recent reviews on MOFs to be guided doing these modifications.
The information on sensor synthesis is also welcome and these data should replace the Section 3 of the manuscript which is unacceptable in the present form due to its textbook character. In fact, the authors can complete this part by MOF examples mentioned in the review or to cut this part and discuss altogether the synthesis and the properties of each MOF that is the best solution, to my opinion (as in page 9, line 397-399 in the present version).
Moreover, the authors commonly give an information on optical response without any discussion of working mechanism. The missing information and scheme should be added.
In each section, MOFs are classified by the nature of metal nodes which commonly do not participate in sensing. To keep this strange organization intact, I propose the authors to add the table in which all MOFs mentioned in Section 4-6 (optical sensors) will be classified according to their working element – bridging organic ligand, bridging metallo-ligand, terminal ligand... In this comparative table the surface properties of MOFs (use n/d when the data are absent), the LOD, linear interval of analyte concentration, working media should be summarized for the commodity of readers. The mechanism of their action and type of response are also welcome.
Next, the discussion should be complete: 1) A comparison of MOFs and corresponding chemosensors are of interest. For example, do TCPP and PCN-224 show a comparative sensing behavior or the immobilization of TCPP in the Zr-framework led to the increase of selectivity and decrease of LOD? 2) It is important to compare different works instead of describe only one of them as in the case the references 121-124 in the present manuscript. 3) it is important first to emphasize common principals used in numerous works as, for example, MOFs bearing thiol receptors for Hg(II) removal and only after to give the examples.
Finally, English is very poor and must be improved.
In fact, the present review is working notes. Additional serious work is needed to compare the reported results and summarized them to get deeper insight into the field under consideration.
Specific comments and suggestions:
Page 1, lines 42-43. Please, revisit the first sentence which has no sense in the present form.
Page 1-2, lines 44-46. Please, complete the list of MOFs applications.
Page 2, line 50-52. Do you need in the discussion of 1D and 2D response ? In fact, these terms are not used in the following discussion. If these terms are important, please, reformulate this sentence because it is unclear.
Figure 1. The Figure is very general to be useful. Hg(II) is drawing as a separated ball incapsulated in a MOF’s cavity. This presentation of sensing and removal mechanism is wrong because both of them are needed in the interaction of Hg(II) ions with metal nodes or linkers.
Section 2. The purpose of this part and choice of the references are unclear. I propose to cut this part and discuss these claims below using real examples.
Page 4, line 170 and numerous similar statements (page 5, line 227, page 6, line 288...). I recommend to avoid personal appreciations if they are free of specific ideas, for example, real examples when this sensor can be also useful.
Page 5, Line 224. Please, explain the role H2O2.
Page 310, line 310 and numerous other (page 8, lines 358, 372, 381...). Please, precise the nature of the competing ions. This important information cannot be summarized in general statement “high selectivity over other competing ions”.
Page 8, line 353. Please, mention ligands one after another: 4,4’-AP = 4,4’-azopyridine, 5-AIA = .... Check all chemical names and do not forget that acids are deprotonated in MOFs.
Page 10, line 471. This MOF can be used for detection of Hg(II) in all samples which are free of Tl(III). Thus, this solid can be accounted as a Hg(II) sensor but this sensor is non-selective. The same remark can be done for the sensors discussed below (page 13, line 606, for example).
Page 10, line 473. What it means “solvent” ?
Page 10, line 482. Please, precise the investigations which you propose or delete this sentence.
Page 10, line 489-495. If this compound is a composite material, why this discussion appears here and not in Section 6? In fact, I do not understand the structure without a figure.
Page 11, line 502. Please, give only whole number (491 and 236). These values cannot be measured with higher precision.
Page 10, line 531. Please, replace “via either fluorescent enhancement or quenching”. Separate the cations into two groups leading to enhancement and quenching, respectively.
Page 11, lines 534-536. The discussion of references 91 and 92 without any figures is unclear. This is an interesting example when a biosensor was incorporated in MOF. How it was done? Which were the advantages compare to the detection by the corresponding biosensor? Please, revisit these works. Should this discussion be moved in Section 6?
Page 12, lines 552,553. The discussion of references 96 and 97 is incomplete and unclear. The structure of MOFs is absent.
Page 12, line 562. MOFs are also metal coordination polymers. Please, explain the difference of solids discussed in Section 4 and 5 more clearly. It seems that non-porous (or non-crystalline ?) metal coordination polymers are discussed in Section 5. Sometimes the information on the porosity is absent in the original work. Thus, the references discussed in Section 4 and 5 cannot be unambiguously classified. Thus, their consideration in a common section seems to be more justify.
Page 15, lines 710-720. Please, give the equation of this decomposition reaction. How Hg(II) triggered the catalytic properties of AuNP?
Page 17, line 793. The discussion of data reported in ref. 122-124 should be added. The LODs of these sensors are excellent and their sensibility is higher than that of most of previously reported T-Hg2+-T- and enzyme-based sensors.
Page 17, line 820. Please, add short description of the nanocomposite structure.
Page 18, line 877. The meaning of Benz is absent in the text.
Figure 8. Add the meaning of coordinated solvent in the caption. The structures of ZrOx, ZrOxyPhos and ZrSulf and the mechanism of Hg(II) removal is unclear from this figure.
Please, revisit the figure, instead of use that was given in the article.
Page 19, line 922. What is it UiO-66-SH?
Page 19, line 926. UiO-66—DMTD shoud be in bold.
Page 19, line 928. The decrease of the sensor surface cannot be regarded as a proof of Hg(II) adsorption (this could be the result of MOF decomposition, for example). Please, change the sentence.
Page 20, line 957. Please, compare the results obtained in ref. 132 and 135. Do the MOFs were prepared by different synthetic procedure? Do their structures and properties were different?
Page 20, line 966. Why this MOPF is more efficient than other thiol-functionalized MOFs?
Section 8. Please, compare all MOFs bearing -SH and -SR functional groups in a table to conclude on the influence of different structural parameters on their efficiency.
Page 21, line 997. The meaning of L1, L2, L3 and L4 is missing.
Page 24, line 1143. L1 and L2 already was used for other ligands (line 997). DMA is also solvent. The solvent meaning is missing.
Page 25, line 1191. Please, discuss this point based on these references. Some MOFs are non-selective and can be used for removal of several toxic metals. This is also important point. The selectivity can be increased by using masking procedures or by introduction of specific functional groups. To my opinion, these references should be discussed in the beginning of this section.
Page 25, line 1194. Why the sensing properties of this material are discussed here and not in the Section “Hg(II) detection and removal” ?
Page 25, line 1205. Please discuss the structure and working mechanism.
Page 25, line 1206. Please discuss the structure and working mechanism.
Page 25, line 1227. Please discuss the structure.
Page 25, lines 1233-1243. Why Fe3O4 is needed?
Page 25, lines 1267-1279. Why In2S3 is needed?
Page 25, line 1340. In fact, most of materials used as sensors can be used for Hg(II) removal. However, the consideration of this question can be omitted by the authors. You should precise that in this section only works in which both aspects were investigated are discussed.
Page 25, line 1354. Please, add the sensing mechanism (colorimetric or luminescent?)
- Advantages and limitations.Please, separate advantages and limitation in two separated lists.
Comments for author File: 
Comments.pdf
Author Response
Reviewer 3:
The review of Kien Wen Sun and co-workers is focused on the detection and removal of mercury ions using MOFs. Mercury is one of the most toxic substances. Inorganic mercury compounds are the most prevalent. Hg2+ ions are bound by both inorganic and organic ligands, and can undergo methylation reaction. Over the past hundred years, the amount of mercury in the upper 100 meters of the world ocean has doubled. The mercury contents in fishes and human hairs in the different countries around the world regularly exceed the maximal levels recommend by the WHO. Thus, development of sensors of this toxic analyte is actual topic in sensing science. The authors carefully look through the recent literature and tried to summarize the reported data. Unfortunately, despite the interest of the topic and excellent list of the references, I cannot recommend this review for publication in the present form. Moreover, I think that in its current state it has serious problems that will take significant efforts to rectify.
“Author Response”
We thank the reviewer for his valuable comment, which allow us to improve our results. We have followed the reviewer’s suggestion and rectified the formal and pointed flaws.
The main problem is that the authors use a descriptive discussion of MOF structures and their actions which is insufficient for modern science. In the best case, the brutto formula of MOFs or metal nodes are given and ligands are named. As a result, a reader has no full information on the organization of the solid. The authors should complete the manuscript by schematic presentation of ALL MOFs and schemes which will allow to understand their synthesis and sensing properties. Please, look through the recent reviews on MOFs to be guided doing these modifications.
“Author Response”
We do agree with the reviewer in regards to provide schemes of MOFs, but providing schemes for all the MOFs may considerably lengthen the pages of the review and affect the readership. Moreover, we have already provided the required information regarding the synthesize of those MOFs in the text. Focus of this review is to deliver the current progress on MOFs-based mercury detection and removal, but not the synthetic schemes of MOFs. Therefore, providing the synthetic schemes of all the MOFs is not possible at this stage.
The information on sensor synthesis is also welcome and these data should replace the Section 3 of the manuscript which is unacceptable in the present form due to its textbook character. In fact, the authors can complete this part by MOF examples mentioned in the review or to cut this part and discuss altogether the synthesis and the properties of each MOF that is the best solution, to my opinion (as in page 9, line 397-399 in the present version). Moreover, the authors commonly give an information on optical response without any discussion of working mechanism. The missing information and scheme should be added.
“Author Response”
Because the section 3 will be more helpful for the readership and other reviewers did not recommend to delete this, therefore, it is unnecessary to remove this section. Information regarding the working mechanism has been upgraded to provide much details in all the sections.
In each section, MOFs are classified by the nature of metal nodes which commonly do not participate in sensing. To keep this strange organization intact, I propose the authors to add the table in which all MOFs mentioned in Section 4-6 (optical sensors) will be classified according to their working element – bridging organic ligand, bridging metallo-ligand, terminal ligand... In this comparative table the surface properties of MOFs (use n/d when the data are absent), the LOD, linear interval of analyte concentration, working media should be summarized for the commodity of readers. The mechanism of their action and type of response are also welcome.
“Author Response”
We agree that providing such comparative table might enhance the manuscript clarity, but it will also lengthen the review and affect the readership. Moreover, we have already provided the required information in the text. Thereby, addition of comparative table is not necessary, which may display duplicated information.
Next, the discussion should be complete: 1) A comparison of MOFs and corresponding chemosensors are of interest. For example, do TCPP and PCN-224 show a comparative sensing behavior or the immobilization of TCPP in the Zr-framework led to the increase of selectivity and decrease of LOD? 2) It is important to compare different works instead of describe only one of them as in the case the references 121-124 in the present manuscript. 3) it is important first to emphasize common principals used in numerous works as, for example, MOFs bearing thiol receptors for Hg(II) removal and only after to give the examples.
“Author Response”
There is no information available for the sensor response of TCPP in the original literature, thus we are unable to compare the sensing performance with PCN-224. Discussion for References 121-124 (currently 129-132) are provided in the revised manuscript. Working principals has been updated in all the sections, however, providing comparative table for MOFs bearing thiol receptors is not possible at this stage.
English is very poor and must be improved.
“Author Response”
We have corrected the lingual deficiencies as per the reviewer’s suggestion.
In fact, the present review is working notes. Additional serious work is needed to compare the reported results and summarized them to get deeper insight into the field under consideration.
“Author Response”
As per reviewer’s suggestion, the manuscript is revised and updated as much as possible with improved discussions.
Specific comments and suggestions:
Page 1, lines 42-43. Please, revisit the first sentence which has no sense in the present form.
Page 1-2, lines 44-46. Please, complete the list of MOFs applications.
“Author Response”
As per recommendation, those sentences and lines were revised and completed.
Page 2, line 50-52. Do you need in the discussion of 1D and 2D response? In fact, these terms are not used in the following discussion. If these terms are important, please, reformulate this sentence because it is unclear.
Figure 1. The Figure is very general to be useful. Hg(II) is drawing as a separated ball incapsulated in a MOF’s cavity. This presentation of sensing and removal mechanism is wrong because both of them are needed in the interaction of Hg(II) ions with metal nodes or linkers.
“Author Response”
Line 50-52: the sentence has been reformulated as per guidelines. Figure 1 is revised according to the possible working mechanism.
Section 2. The purpose of this part and choice of the references are unclear. I propose to cut this part and discuss these claims below using real examples.
“Author Response”
Because the section 2 will be more helpful for the upcoming researchers and other reviewers did not recommend to delete this, therefore, it is unnecessary to remove this section.
Page 4, line 170 and numerous similar statements (page 5, line 227, page 6, line 288...). I recommend to avoid personal appreciations if they are free of specific ideas, for example, real examples when this sensor can be also useful.
“Author Response”
As per guidelines, those personal appreciations were avoided.
Page 5, Line 224. Please, explain the role H2O2.
“Author Response”
The role of H2O2 is mentioned in the text (as the masking agent for Fe3+).
Page 7, line 310 and numerous other (page 8, lines 358, 372, 381...). Please, precise the nature of the competing ions. This important information cannot be summarized in general statement “high selectivity over other competing ions”.
“Author Response”
As requested, the general statement “high selectivity over other competing ions” has been revised with precision in all these lines.
Page 8, line 353. Please, mention ligands one after another: 4,4’-AP = 4,4’-azopyridine, 5-AIA = .... Check all chemical names and do not forget that acids are deprotonated in MOFs.
“Author Response”
As suggested, those ligand names are mentioned one after another.
Page 10, line 471. This MOF can be used for detection of Hg(II) in all samples which are free of Tl(III). Thus, this solid can be accounted as a Hg(II) sensor but this sensor is non-selective. The same remark can be done for the sensors discussed below (page 13, line 606, for example).
Page 10, line 473. What it means “solvent”?
Page 10, line 482. Please, precise the investigations which you propose or delete this sentence.
Page 10, line 489-495. If this compound is a composite material, why this discussion appears here and not in Section 6? In fact, I do not understand the structure without a figure.
“Author Response”
Line 471 and 606: the text is updated as suggested by the reviewer.
Line 473: the meaning of solvent (DMF = Dimethylformamide) is provided.
Line 482: the sentence is deleted as suggested.
Line 489-495: As per suggestion those sentences are move to section 6.
Page 11, line 502. Please, give only whole number (491 and 236). These values cannot be measured with higher precision.
Page 11, line 531. Please, replace “via either fluorescent enhancement or quenching”. Separate the cations into two groups leading to enhancement and quenching, respectively.
Page 11, lines 534-536. The discussion of references 91 and 92 without any figures is unclear. This is an interesting example when a biosensor was incorporated in MOF. How it was done? Which were the advantages compare to the detection by the corresponding biosensor? Please, revisit these works. Should this discussion be moved in Section 6?
“Author Response”
Line 502: all the BET surface area numbers are given as whole number as per recommendation.
Line 531: It is not possible to write the sentence as suggested by the reviewer, because mercury and Lead displays the fluorescent enhancement or quenching response (by modulating the exciting wavelengths) and other ions shows quenching. Thus, separate the cations into two category and writing as suggested is not possible for this case.
Lines 534-536: References 91 and 92 (currently Refs 113 and 114) are moved to section 6 with required discussion and the new figure (Figure 6) is provided as per recommendation.
Page 12, lines 552,553. The discussion of references 96 and 97 is incomplete and unclear. The structure of MOFs is absent.
“Author Response”
Lines: 552, 553: The structures of references 96 and 97 (currently 99 and 100) are provided. However, the discussion is unnecessary because their deficiency in the selectivity and other properties.
Page 12, line 562. MOFs are also metal coordination polymers. Please, explain the difference of solids discussed in Section 4 and 5 more clearly. It seems that non-porous (or non-crystalline?) metal coordination polymers are discussed in Section 5. Sometimes the information on the porosity is absent in the original work. Thus, the references discussed in Section 4 and 5 cannot be unambiguously classified. Thus, their consideration in a common section seems to be more justify.
“Author Response”
We divided the references in the section 4 and 5 as per the reference title and authors statements available in those references. We did not divide them by porosity or crystallinity. The classifications are based on the justification of authors from the original references.
Page 15, lines 710-720. Please, give the equation of this decomposition reaction. How Hg(II) triggered the catalytic properties of AuNP?
“Author Response”
Line 710-720: There is no equation available in the original manuscript, thus providing the equation for catalytic properties is not possible. However, we already discuss the details in text for readers’ clarification.
Page 17, line 793. The discussion of data reported in ref. 122-124 should be added. The LODs of these sensors are excellent and their sensibility is higher than that of most of previously reported T-Hg2+-T- and enzyme-based sensors.
Page 17, line 820. Please, add short description of the nanocomposite structure.
“Author Response”
Line 793: the discussions for Refs 122-124 (Currently Refs 130-132, lies 811-829) are provided in section 6.
Page 18, line 877. The meaning of Benz is absent in the text.
Figure 8. Add the meaning of coordinated solvent in the caption. The structures of ZrOx, ZrOxyPhos and ZrSulf and the mechanism of Hg(II) removal is unclear from this figure. Please, revisit the figure, instead of use that was given in the article.
“Author Response”
Line 877: The meaning of Benz is updated.
Figure 8: The figure caption is updated with required information.
Page 19, line 922. What is it UiO-66-SH?
Page 19, line 926. UiO-66—DMTD shoud be in bold.
Page 19, line 928. The decrease of the sensor surface cannot be regarded as a proof of Hg(II) adsorption (this could be the result of MOF decomposition, for example). Please, change the sentence.
“Author Response”
Line 922: The meaning of UiO-66-SH is provided.
Line 926: UiO-66-DMTD is bolded.
Line 928: The sentence has been modified according to suggestion.
Page 20, line 957. Please, compare the results obtained in ref. 132 and 135. Do the MOFs were prepared by different synthetic procedure? Do their structures and properties were different?
Page 20, line 966. Why this MOPF is more efficient than other thiol-functionalized MOFs?
“Author Response”
Line 957: Since those MOFs were synthesized using similar synthetic tactics, comparison is not meaningful.
Line 966: This is because that it has the dense thiol arrays, thus become more efficient. This discussion is already in the text.
Section 8. Please, compare all MOFs bearing -SH and -SR functional groups in a table to conclude on the influence of different structural parameters on their efficiency.
“Author Response”
We have already provided the required information in the text. Therefore, addition of comparative table or comparative discussion on MOFs bearing -SH and -SR is not necessary. Moreover, our intention is to provide information regarding the ongoing progress on MOFs-based mercury detection and removal but not to justify the best one.
Page 21, line 997. The meaning of L1, L2, L3 and L4 is missing.
Page 24, line 1143. L1 and L2 already was used for other ligands (line 997). DMA is also solvent. The solvent meaning is missing.
“Author Response”
Line 997: The meaning of L1 to L4 is provided in the text.
Line 1143: we provide the MOF structure as stated in the original reference, we did not provide any name in our own. These L1 and L2 are different and their meanings are provided as well. The meaning of DMA is also delivered in the text.
Page 25, line 1191. Please, discuss this point based on these references. Some MOFs are non-selective and can be used for removal of several toxic metals. This is also important point. The selectivity can be increased by using masking procedures or by introduction of specific functional groups. To my opinion, these references should be discussed in the beginning of this section.
Page 25, line 1194. Why the sensing properties of this material are discussed here and not in the Section “Hg(II) detection and removal” ?
Page 25, line 1205. Please discuss the structure and working mechanism.
Page 25, line 1206. Please discuss the structure and working mechanism.
Page 25, line 1227. Please discuss the structure.
Page 25, lines 1233-1243. Why Fe3O4 is needed?
Page 25, lines 1267-1279. Why In2S3 is needed?
Page 25, line 1340. In fact, most of materials used as sensors can be used for Hg(II) removal. However, the consideration of this question can be omitted by the authors. You should precise that in this section only works in which both aspects were investigated are discussed.
Page 25, line 1354. Please, add the sensing mechanism (colorimetric or luminescent?)
“Author Response”
Line 1191: Since those references are non-selective, there is no meaning to discuss them in detail and is unnecessary to move them to the beginning of the section.
Line 1194: Those references are discussed for mercury removal because authors of those original manuscript emphasized removal processes more than detection.
Lines 1205, 1206: The structure and mechanism were already discussed in the text.
Line 1227: The structure has been mentioned for clarity.
Lines 1233-1243: The Fe3O4 was included to improve the magnetic property of MOF system, which played a vital role in the mercury removal.
Lines 1267-1279: In2S3 nanoparticles were included to improve the efficiency of mercury removal.
Line 1340: This section is based on the manuscript title and statement provided by authors of the original manuscript.
Line 1354: the mechanism has been mentioned in the text.
- Advantages and limitations. Please, separate advantages and limitation in two separated lists.
“Author Response”
Advantages and Limitations section is divided into two separate section as suggested by the reviewer.
Round 2
Reviewer 2 Report
The authors have satisfactory revised the script.
Author Response
We thank reviewer's valuable comments.
Reviewer 3 Report
The revision is incomplete.
The main problem is that the authors use a descriptive discussion of MOF structures and their actions which is insufficient for modern science. In the best case, the brutto formula of MOFs or metal nodes are given and ligands are named. As a result, a reader has no full information on the organization of the solid. The authors should complete the manuscript by schematic presentation of ALL MOFs and schemes which will allow to understand their synthesis and sensing properties. Please, look through the recent reviews on MOFs to be guided doing these modifications.
I propose the authors to add the table in which all MOFs mentioned in Section 4-6 (optical sensors) will be classified according to their working element – bridging organic ligand, bridging metallo-ligand, terminal ligand... In this comparative table the surface properties of MOFs (use n/d when the data are absent), the LOD, linear interval of analyte concentration, working media should be summarized for the commodity of readers. The mechanism of their action and type of response are also welcome.
Without these two modifications the review cannot be published.
Author Response
Response for the reviewer’s comments
The main problem is that the authors use a descriptive discussion of MOF structures and their actions which is insufficient for modern science. In the best case, the brutto formula of MOFs or metal nodes are given and ligands are named. As a result, a reader has no full information on the organization of the solid. The authors should complete the manuscript by schematic presentation of ALL MOFs and schemes which will allow to understand their synthesis and sensing properties. Please, look through the recent reviews on MOFs to be guided doing these modifications.
“Author Response”
We do respect the reviewer’s comments regarding adding schemes of MOFs. However, many recent reviews on MOFs based sensors also did not provide all the synthetic schemes of MOFs. First of all, to provide the schemes of ALL MOFs, we need to obtained permissions from publishers of those original publications (nearly 120 references). Adding those MOFs schemes and explanations for those schemes will lengthen the manuscript (is estimated over 70 pages) and affect the uniqueness and readership. Moreover, some manuscript did not have any synthetic schemes, in such cases we do not know how to provide their synthetic schemes. Since our intention is to provide the ongoing progress on MOFs-based mercury detection and removal, we have already provided the essential information for the readers. Therefore, it is not necessary to provide the synthetic schemes and explanations of all the MOFs. Even we plan to do so, it will not be accomplished without giving reasonable time.
I propose the authors to add the table in which all MOFs mentioned in Section 4-6 (optical sensors) will be classified according to their working element – bridging organic ligand, bridging metallo-ligand, terminal ligand... In this comparative table the surface properties of MOFs (use n/d when the data are absent), the LOD, linear interval of analyte concentration, working media should be summarized for the commodity of readers. The mechanism of their action and type of response are also welcome.
“Author Response”
We do respect the reviewer’s comments regarding adding a comparative table. Since our intention is to deliver the ongoing progress MOFs-based mercury detection and removal but not to justify the best one, which has been discussed clearly in the text. Therefore, we think to provide such table is not necessary. There is no need of personal appreciations, comparison and ideas for certain cases as stated by the reviewer. Moreover, adding those comparative tables will lengthen f the manuscript and affect the uniqueness and readership. Moreover, we have already provided the required information in the text.
